Global Warming may proceed faster than expected

1 05 2015…

There certainly is some evidence that climate sensitivity may be below 2°C. But if you look at all of the evidence, it’s hard to reconcile with such a low climate sensitivity. I think our best estimate is still around 3°C for doubled CO2.

Mark Cochrane has this to say about the above……..:

The above video and article at the link do a good job laying out the range and likelihood of various modelled climate sensitivities to a doubling of pre-industrial atmospheric carbon levels. The extension of the published IPCC range of possible sensitivities to values as low as 1.5C are more an exercise of political correctness than anything else. To realistically have values below about 2.5C you would need to have both reduced feedbacks (e.g. increasing water vapour in the atmosphere and melting ice cover on the ground) and a large negative feedback from clouds (e.g. more low level clouds at low latitudes).

The problem for this scenario being that we have already had decades of measurements that positively show the feedbacks we have already gotten, in terms of increased water vapour and decreased ice cover, won’t support a low climate sensitivity. Similarly, the clouds haven’t shown up as hoped. I spent about 15 years assuming and hoping that they would. Reality and various research studies beat that idea out of my head. If anything, the clouds are yielding a small positive feedback (warming). Depending who you believe that could be due to wispy high level clouds that trap heat or diminished low level clouds at lower latitudes that reflect less sunlight.  Could be a bit of both.

So, barring a sudden and unexpected change in all of the trends to our advantage, a climate sensitivity below 2.5C is a pipe dream. Something more like 3-3.5C is probable with higher values more likely than lower ones around that range. Note, I’d really like to be proven wrong about this… (to the low side)

In practical terms, the higher the climate sensitivity, the faster and more extreme the emissions cuts we will have to make in order to avoid compromising the resilience of our society and the rest of global ecosystems to climate changes as we progress through this century.

Wishful thinking is not a viable strategy for managing our future.




One response

2 05 2015
Anthony William O'brien

Wishful thinking is all we have left. Civilization is going away the minute the wishful thinking stops. The bad news; we have probably reached peak wishful thinking.

As we spin around with our fingers in our ears shouting not true, not true, reality is kicking us in the goolies. Soon reality will get our attention.

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